Help with Shimano Bottom Brackets?

Folks,

I have a relatively standard square taper Shimano BB-UN52 of bottom
bracket. The lock ring goes on the left (non-drive) side, which may be
important to this story of woe. It has a spindle length of 107 mm.
http://sheldonbrown.com/harris/bottombrackets.html

I need to move my drive side out by about 2 or 3 mm to get a correct
chain line. I've added a thicker, aluminum inner chain ring to my
triple and now it's hitting the chainstay.

I've obtained another BB-UN with a 110mm spindle.

Unfortunately, the difference in the spindle length is all on the
left, non-drive side, so it doesn't do anything to improve my chain
line.

I've fasioned a crude 2mm shim, which I've place over the 110m BB on
the drive side. When installed, this moves the drive side out to the
correct distaince giving me perfect clearance for the inner rings from
the chainstay and a 45mm distance (Shimano spec) from center of the
seat tub to the center of the middle ring teeth.

But, this means that the left side, non-drive side locking ring goes
inside the BB shell by 1-2 mm exposing that amount of BB threads.

I'm afraid of those threads rusting up over time.

Questions...

1) Do all Shimano square taper BB give the same amount of spindle
length on the right, drive side? If so, how is one supposed to adjust
chain line (other than my crude fudge)?

2) Am I right to be concerned about the exposed thread in the BB
rusting up when exposed like this? (the frame is steel)

Thanks for any help,


-- Dave
==============================================
"It is impossible, or not easy, to do noble acts
without the proper equipment."
Aristotle, Politics, 1323a-b, trans Jowett
==============================================

pinnah wrote:
Folks,

I have a relatively standard square taper Shimano BB-UN52 of bottom
bracket. The lock ring goes on the left (non-drive) side, which may be
important to this story of woe. It has a spindle length of 107 mm.
http://sheldonbrown.com/harris/bottombrackets.html

I need to move my drive side out by about 2 or 3 mm to get a correct
chain line. I've added a thicker, aluminum inner chain ring to my
triple and now it's hitting the chainstay.

I've obtained another BB-UN with a 110mm spindle.

Unfortunately, the difference in the spindle length is all on the
left, non-drive side, so it doesn't do anything to improve my chain
line.

I've fasioned a crude 2mm shim, which I've place over the 110m BB on
the drive side. When installed, this moves the drive side out to the
correct distaince giving me perfect clearance for the inner rings from
the chainstay and a 45mm distance (Shimano spec) from center of the
seat tub to the center of the middle ring teeth.

But, this means that the left side, non-drive side locking ring goes
inside the BB shell by 1-2 mm exposing that amount of BB threads.

I'm afraid of those threads rusting up over time.

Questions...

1) Do all Shimano square taper BB give the same amount of spindle
length on the right, drive side? If so, how is one supposed to adjust
chain line (other than my crude fudge)?

Adjust chainline with an actual BB/freewheel spacer. Bike shops have
them.

2) Am I right to be concerned about the exposed thread in the BB
rusting up when exposed like this? (the frame is steel)

Nope. One of my commuters has been this way for years. No problems.
If you're riding in nasty weather, you should be pulling and regreasing
the BB periodically anyways.

-Vee

important to this story of woe. It has a spindle length of 107 mm.

I've obtained another BB-UN with a 110mm spindle.

Unfortunately, the difference in the spindle length is all on the
left, non-drive side, so it doesn't do anything to improve my chain

Is this considered normal, or a defective part??

Shouldn't the lenght of the spindle be the same on both sides??

jbr

"pinnah" a écrit:

1) Do all Shimano square taper BB give the same amount of spindle
length on the right, drive side? If so, how is one supposed to adjust
chain line (other than my crude fudge)?

Not all Shimano BBs have the same right side offset. John Barnett has a
table of relative chainline for various models in his manual. The relevant
chapter is available for free download:

http://www.bbinstitute.com/manual.htm#order/download3

Chain line is often adjusted with a spacer, either one made for the purpose,
or a freewheel/cassette or Sturmey Archer sprocket spacer.

2) Am I right to be concerned about the exposed thread in the
BB rusting up when exposed like this? (the frame is steel)

Keep it greasy. I don't think you need to lose any sleep.

James Thomson